This invention relates to the separation of particulate from the gas, derived from the combustion of fossil fuel, which drives the turbine of a power plant. Typically, it is required that the particulate in the driving gas be reduced to 15 parts per million or less. This invention has particular relationship to the separation of particulate from the gas of pressurized fluid-bed combustion systems in which the combustion of the fuel and the removal of the particulate is integrated into a single large pressure vessel. In this application this vessel will be sometimes referred to as the "main vessel" to distinguish from auxiliary vessels mounted within the main vessel. This invention as applied to systems in which the combustion and particulate separation are integrated is unique and has significant advantages. But it is to be understood that to the extent that this invention in any of its aspects finds adaptation to power plants in which the combustion and particulate are not integrated, such adaptation is within the scope of equivalents of this application and of any patent or patents which may issue on or as a result thereof. The word "particulate" as used in this application is intended to comprehend within its scope both solid and liquid particulate.
In a typical pressurized fluid bed power generating system in which the combustion and particulate separation are integrated, the gas from the combustion which is to be processed for particle separation contains about 15,000 parts per million by mass of particulate. It is required that the outlet gas supplied to the turbines shall contain only 15 ppm or less.
Pressurized fluid bed combustion systems, in accordance with the teachings of the prior art, in which combustion and particulate separation are integrated includes in the separation chambers pairs of cyclones, each pair operating in series. The cyclone pairs are capable of separating particles whose diameter, or greatest cross dimension, exceeds about 10 microns and to reduce the particulate to about 300 ppm or more by mass. To meet the requirement of 15 ppm or less, it has in the prior-art practice been found necessary to include an electrostatic precipitator or a conventional bag-house filter for removing the residual particulate from the cold turbine exhaust gas. Because the turbines exhaust gas is substantially at atmospheric pressure, and high volumetric flow, a precipitator of large area or a large bag-house filter is demanded to meet this requirement.
It is an object of this invention to overcome the disadvantages and drawbacks of the prior art and to provide a combustion system for power generation in which the combustion and particulate separation are integrated and in whose use the particulate separation effected in the separation chamber shall reduce the particulate content in the processed gas to the required low magnitude thus dispensing with the demand for an electric precipitator or other facility house filter. It is also an object of this invention to provide a method for operating a combustion system in which the combustion and particulate separation are integrated in whose practice the particulate content of the processed gas shall meet the requirement for low particulate content.